Gd2-xSmxZr2O7 (x=0, 0.2, 0.6, 1.0, 1.4, 1.8, 2.0) ceramic powders synthesized with the chemical-coprecipitation and calcination method were pressureless-sintered at 1873 K for 10 h in air. The electrical conductivity of Gd2-xSmxZr2O7 ceramics was investigated by complex impedance spectroscopy over a frequency range of 0.01 Hz to 15 MHz. Gd2-xSmxZr2O7 is an oxide-ion conductor in the oxygen partial pressure range from 1.0 x 10(-15) to 1.0 atm and in the temperature range of 623-873 K. The measured electrical conductivity obeys the Arrhenius relation. The activation energy and pre-exponential factor for grain-interior conductivity gradually decrease with increasing Sm content. The grain-interior conductivity varies with the Sm substitution for Gd, and reaches the maximum at the equal molar of Sm and Gd3+ in Gd2-xSmxZr2O7 ceramics. A significant increase in the grain-interior conductivity is obtained by isovalent rare-earth element like Sm Substitution for Gd in the temperature range of 623-873 K. (C) 2008 Elsevier B.V. All rights reserved.